Rotary cutting tools, such as end mills, typically have a cylindrical configuration that includes a shank portion and a cutting portion. The cutting portion contains a plurality of helically disposed cutting blades that extend from a first end (i.e., the “shank end”) of the cutting portion adjacent the shank portion, toward the opposite end (i.e., the “free end”) of the cutting portion. In some embodiments, the cutting edges of the helical blades are disposed along a substantially constant radius with respect to the longitudinal axis of the tool. In other embodiments, generally referred to as “tapered” cutting tools, the cutting portion is substantially frustoconical in shape; i.e., the cutting edge of each blade has a constantly decreasing radius with respect to the longitudinal axis of the tool as the cutting edge extends from the shank end of the cutting portion to the free end. The cutting edges of the blades in a tapered rotary cutting tool are at the same radius from the longitudinal axis of the tool in any plane through the cutting portion and perpendicular to the longitudinal axis of the tool. In still other end mill embodiments, generally referred to as “straight-fluted” rotary cutting tools, the cutting edges of the blades extend parallel to the longitudinal axis of the tool.
There are several inherent problems in the use of any of the conventional rotary cutting tools described above. Generally, these problems manifest themselves in excessive wear and relatively poor cutting actions, or both, due to the fact that the entire length of the cutting edge may be applied to the workpiece at the same time, and due to the fact that continuous chips are produced which are not adequately removed from the work area. There have been many attempts to improve the cutting action and decrease the wear in such tools, and these attempts usually involve the use of so called “chip breakers” in the form of relatively deep notches cut transversely into the cutting blade in a pattern at spaced intervals, or some similar form of providing an interrupted cutting edge along each blade.
A conventional chip breaker pattern for a six-fluted end mill design is shown in FIG. 8. As seen, the typical chip breaker pattern is such that a chip breakers on one blade, for example, blade #2 are directly behind the chip breakers on the adjacent blades #1 and #3 for a particular length-of-cut (LOC). The point, P, where the blade transitions back into the cut is a critical part of the geometry and is typically where tool failure occurs. Because this transition point is directly behind a chip breaker, this critical area of the tool has twice the amount of the programmed chip load per blade, which results in this area being even more prone to failure. Therefore, it is desirable to provide a rotary cutting tool that overcomes the shortcomings of the prior art.